1. Field of the Invention
This invention relates to a melt process for the synthesis of poly(metal aromatic ester) resin compositions, and more particularly relates to an improved process for making poly(metal aromatic ester) resins wherein the byproducts formed thereby are volatile.
2. Description of the Related Art
Poly(metal aromatic ester) resins such as calcium terephthalate polymers, zinc terephthalate polymers and tin terephthalate polymers are known, and are in use as additives for thermoplastic compositions because of properties such as their use as scavengers for traces of water, their use as polymeric lubricants, their use as activators for sulphur accelerator crosslinking systems, and their use for generating intumescent char in such compositions. Suitable resins compositions for incorporating the above additives include polypropylene compositions, polyester compositions, and elastomeric compositions such as styrene butadiene rubber and EPDM.
Method for making poly(metal aromatic ester) resins include such known processes as reaction of an aqueous solution of metal terephthalate, for example, sodium terephthalate, with an aqueous stanous halide solution, to form poly(stanous terephthalate) and sodium halide (metal halide salt). The polymer formed precipitates out of solution and is difficult to further purify due to its solvent resistance. Thus metal halide salt trapped in the polymer matrix cannot be removed thereby posing contamination problems. The product thus formed has metal halide salts contaminates in excess of 100 parts per million by weight.
Accordingly, there is a need to provide an improved method for making poly(metal aromatic ester) resins which leads only to volatile byproducts being developed, and being free of non-volatile byproducts in the poly(metal aromatic ester) resin.